Storage type cathode-ray tube



March 15, 1949. SNYDER, {R 2,464,420

STORAGE TYPE CATHODE-RAY TUBE Filed Dec. 31, 1943 IN VEN TOR.

L NYDERJR Patented Mar. 15, 1 949 STORAGE TYPE CATHODE-RAY TUBE RichardL. Snyder, Jr., Princeton,

N. J assignor to Radio Corporation of America, a corporation of DelawareClaims. 1

This invention relates to electron discharge devices and particularly toimprovements in pluralbeam cathode ray tubes of the type suitable foraveraging-out noise in radar and analogous systems for the communicationof intelligence.

In the use of radar and similar equipment the received signals are oftenaffected by static and other undesired extraneous electricaldisturbances. Usually, radar and other pulse signal trains are identicalover a large number of operatingcycles and it has previously beenproposed to employ a tube capable of storing a large number of thesecycles in such a manner that the noise fluctuations (which are usuallyrandom in character) will integrate to some value close to zero, whilethe signals, which occur at regular intervals, are reinforced. When thestored cycles are reproduced, the various Wanted parts of the signalcoincide and produce considerable improvement in the signal-to-noiseratio.

- Such noise reduction systems usually employ a plural-beam cathode raytube for averagingout the noise and these tubes may be provided withstorage electrodes of various types. By way of example: the storageelectrode may comprise a two-sided mosaic, in which case the put-on andtake-off beams are directed upon opposite sides of the screen (seeBritish Patent 501,179). Another tube heretofore employed in such anoise reduction system employs a single-sided eaesiated screen ofspecial (commutator type) laminated construction. In this case bothbeams may impinge upon the same side of the screen, preferably atdifferent velocities (as to this see copending application, Serial No.492,658, filed June 26, 1943). Alternatively, (as shown in applicationSerial No. 496,741, filed July 30, 1943, now U. S. Patent 2,416,914,issued March 4, 1947) the storage screen may comprise a multiplicity ofspaced capacitor armatures upon which the signal is impressed by onebeam, the second beam being arranged to scan the inter-armature space ina manner calculated to take-01f the signal.

Irrespective of the advantages claimed for the plural-beam cathode raytubes of the prior art, it may be said generally that the insulation andother problems incident to the construction and use of their mosaictype, commutator type and multi-capacitor type? signal-storageelectrodes renders such tubes more complicated and expensive than is nownecessary or desirable.

Accordingly, the principal object of the present invention is to providean improved plural-beam cathode ray tube capable of averaging-outundesired components from the signal waves or pulses in radar, radio andanalogous systems for the communication of intelligence, said tube beingcharacterized by the simplicity and economy of its parts and by itstrouble-free performance.

Other objects and advantages will be apparent and the invention itselfwill be best understood by reference to the following specification andto the accompanying partly diagrammatic sectional view of a plural-beamcathode ray tube embodying the invention.

As indicated in the drawing, the present invention contemplates and itspractive provides a plural beam tube having a storage electrodeconstituted simply of a sheet I of mica or equivalent (1. e. opaque toelectrons) insulating material and a conductive signal plate or film 3which is mounted on or contiguous the back of the said insulating sheet.This storage electrode I, 3, is mounted in the bulbous portion 5 of ahighly evacuated tube or envelope I. The tube 1 is provided with twodependenthollow neck portions 9 and I I, within which the electron gunsII! and I2, respectively, are separatel mounted. These guns" I 0 and I2may be of conventional construction and, in any event, are each providedeither with a pair of horizontal and a pair of vertical deflectingplates IIJH, IZH; IIlV, I2V, respectively, or with magnetic deflectingmeans for imparting a scanning movement to the electron beams from theseparate guns Ill and I2. As in standard practice, grounded metalliccoatings I3 and I5 on the inner surface of the tube serve as the secondanodes for the guns II) and I2 respectively.

The electron axis of the gun it is arranged at an angle of substantiallywith respect to the plane of the target surface of the mica sheet I;thus its beam l4 strikes the said surface with normal incidence. Theaxis of the other gun I2 is elf-set slightly less than 90 from the axisof the gun III and is thus disposed at an acute angle (of from, say, 1,to say, 10) with respect to the plane of the target. The beam I6 fromthe gun l2 bombards the same ora slightly larger area, of the targetsurface I as does the beam I4 from the gun I0, but with grazingincidence.

The bombarded side of the mica target I is shielded by a pair of spacedapart plates I8, I8 which are arranged in parallel relation on oppositesides of the path of the beam I4, and out of the path of the beam I6.These plates I8, I8 are thus so arranged that they control theelectrostatic field on the gun side of the target; they also serve :ascollector electrodes for secondary electrons from the said target.

The relative potential distribution among the several electrodes ispreferably (but not neces, sarily) as follows: gun cathodes2000 volts,grid bias 9 to, say, 50 volts first anodes-4700 volts second anodes,collector plates (I8, I8) and signal plate (3) at about groundpotential.

In operating the device of the invention, the

beam I4 is adjusted to such ahigh velocity that. the ratio of thesecondary electrons to the primary electrons is less than unity. Thebeam I6, which strikes the target with grazing incidence, has the samevelocity as the beam I4 but because it is grazing, as is well known, thesecondary emission ratio will be greater than unity. Therefore, thenormal beam I4 will act to charge the surface of the mica negative withrespect to the col,- lectors I8, I8 because the number of secondaryelectrons leaving the surface of the mica will be less than the numberof primary electrons. bombarding it. The opposite condition existsin.the region. bombarded by. the grazing electron beam I6. The grazing beam(I6) carries sufficient current at all times to overcome themaximumnegative charge that the normal beam I4 can put on thetarget.

In operation, the static affected signal-bearing waves are applied tothe" grid ItiG of the gun I0. and modulate the beam It. and thesaidvbeam is. deflected horizontally with, a linear sweep. at the samefrequency as that of the operating. cycle of the radar or otherequipment with. which the tube l is associated. In addition, in. order.to spread the charged area on. the target I. for the dual purpose ofstoring more charge and enlarging thestorage area, this beam (I4) isdeflected in the vertical direction by a high frequency, voltage (whichis applied to the verticaldeflecting plates 58V ina well-known. manner)well above any frequency which. might be present in the signal. Thegrazing beam I6, is unmodulated but is preferably similarly spread orfuzzedf so that its vertical displacementis. the sameor greater than.that of the normal beam I4. The horizontal deflection of the grazingbeam Ifi. is equal in amplitude and character tothatof the normal beam94. but, is preferably very much lower in frequency. Under theseconditions,.the normal beam puts the signal on the storage electrodemany times in the per-iodof horizontal deflection of the grazing ortake-off. beam I61 As mentioned above, the-grazing; beam Ifi-can alwayscharge the mica surface I of: theitarget to the collector potential.Thus, as the said-beam I6 sweeps slowly over each portion of the targetsurface which has been charged by the normal beam it, each of.saidportionsisdischarged and a displacement current flows, in. thecircuit of the back-plate 3. This displacement current. is a very lowfrequency facsimile of the original signal in which the-noise or static;is-integrated or; balanced-out. The nQise-free-signal may; then beamplified in the; usual manner and; viewed either with a cathode rayoscilloscope; (not shown): having a lougrpersistent screen, or: it-

may be otherwise recorded as on a facsimile machine (not shown).

It will be apparent from the foregoing that the present inventionprovides an improved plural beam cathode ray tube capable ofaveragingout" undesired components from the signal surface or pulses inradan'radi-o and analogous systems for the communication of intelligenceand that said tube is characterized by thesimplicity and economy of itsparts and by its trouble-free performance.

It may also find application in instances wherein it is desirable tochange the frequency of a radar signal. This need occurs when theoutputs of a number of radar equipments situated in different locationsmust be correlated at a central station. Under these circumstances thehigh frequency radar signals are recorded at their normal speed andtaken off the record at a much slower speed suitable for transmissionover telephone lines.

I, claim as my invention:

1'. A storage electrode for a plural beam cathode ray tube, said storageelectrode comprising a target consisting only of' an insulating materialwhich is opaque to electrons and a conductive backplate for saidinsulating target.

2. The invention. as set forth in. claim 1 and wherein said insulatingmaterial consists only of mica.

3. A storage device comprising an evacuated envelope-containing a.storage electrode consistingv only of an insulating surface whichisopaque t o.electrons.and a conductive backplate. for said surface,means for generating a plurality of beams of. electrons within saidenvelope, and means. for directing said plurality of electron beams,simultaneously, upon said. electron opaque insulating surface.

4. A storage device comprising an evacuated envelope containing astorage. electrode. comprising a. plane surface consisting only ofaninsulating material which is opaque to electrons anda conductivebackplate for said surface, and a.

plurality of electron guns. mounted to project: their electronsontheexposed side of said-insulating surface.

5. The invention. asset forth in claim, 4 and wherein the. axis of oneof the said electron guns is disposed at an angle of substantially. 90with respect tov said insulating surface and the axis of the other ofsaid electron guns. ismounted at, an acute angle with respect to said.surface.

6.. A. storage device comprising an evacuated. envelopecontaining astorage electrode consisting; only of. an insulating surface. whichis-opaque. to. electrons andaconductive backplate for saidzsure face,means. for generating a. plurality. of. beams of. electrons within saidenvelope, means for. directing said electron beams upon said electronopaque insulating surface withv sufiicient velocity to. cause theemission of secondary-electrons. therefrom, and means for collecting,said sec..- on'dary-electrons.

'7. The invention as set forth in claim 6- and: wherein said collectingmeans comprises a pair of-metal plates mounted in spaced parallel arrayon opposite sides of thepath of one of said beams and out-off the pathof the other of said beams.-

8. An electrondischarge devicecomprising an evacuated" envelopecontaining an: electron gun; atarget consisting only. of; an. insulatingsurface. mountedin a: plane substantially normal-tothe axis of: saidgun. and upon which. primary-elem trons fromssaida gun are adapted: to:impinge with:

a velocity calculated to release not more than one secondary-electronfor each impinging primary electron, a. second electron gun mountedalong an axis which forms an acute angle with said target surface andadapted to project a second stream of primary-electrons upon said targetsurface with a, velocity and at an angle calculated to release more thanone secondary-electron for each impinging primary-electron from saidsecond stream, and a metal backplate for said target to which adisplacement current is adapted to fiow when said target surface issubjected to bombardment with primary electrons from both of saidelectron guns.

9. The invention as set forth in claim 8 and wherein said firstmentioned electron-gun is provided with means for directing its streamof electrons across said target at a certain rate and said secondmentioned electron-gun is provided with means for directing its streamof electrons across said target at a slower rate.

10. The invention as set forth in claim 8 and wherein means are providedfor impressing a signal upon said first mentioned electron stream.

RICHARD L. SNYDER, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

5 UNITED STATES PATENTS Number Name Date 2,108,097 Bedford et a1 Feb.15, 1938 2,122,095 Gabor June .28, 1938 10 2,147,760 Vance et a1 Feb.21, 1939 2,156,992 Iams May 2, 1939 2,264,549 Lubszynski Dec. 2, 19412,280,191 Hergenrother Apr. 21, 1942 2,324,534 Pierce July 20, 19432,339,662 Teal Jan. 18, 1944 2,366,319 Donal, Jr. Jan. 2, 1945 FOREIGNPATENTS Number Country Date 481,170 Great Britain Mar. '7, 1938

